What is important for the power factor

Power factor

The power factor, Power Factor (PF), is a measure of the inductive or capacitive load, which in the case of sinusoidal voltages is expressed in the phase shift between current and voltage. Mathematically, it is the quotient of active power (P) and apparent power (S). This quotient is designated with the Greek lambda and corresponds to the cosine Phi between the two powers.


The power factor can assume values ​​between 1 and 0, depending on whether the load is ohmic, a reactance, i.e. a purely inductive or capacitive resistance, or an impedance consisting of an effective resistance and a reactance. With a purely ohmic resistor, the voltage and current are in phase, it is an active power and the power factor is "1". This power factor occurs, among other things, with electrical heaters and incandescent lamps.

If a phase shift occurs between the two quantities, then it is a matter of a reactance, the imaginary part of which determines the phase shift. If there is a phase shift of 90 ° between the two quantities, it is purely apparent power and the power factor is "0". Electrical devices with high inductive reactance include motors, transformers, relays, etc. The power factor is a variable that is important for the power consumption of power supplies. The values ​​for the power factors can be measured with power factor measuring devices. They show the capacitive and inductive deviations as cosine Phi. In addition to the power factor, there is also the reactive power factor. This corresponds to the sine phi of the ratio between reactive power and apparent power. The reactive power factor is calculated from the ratio between reactive power and apparent power. A higher reactive power factor results in a lower active power factor.